In the prior art, a coupler draft gear used in railway carriages includes two kinds such as a fixed coupler draft gear and a rotatable coupler draft gear, and a coupler yoke is the most important part of the coupler draft gear. The railway carriages are connected by a coupler, and the coupler is connected with the coupler yoke by a coupler yoke key, so that the connection between the wagons of a train is ensured, and the wagons constitute the train for transmitting tractive force in transportation. There are two kinds of coupler yokes, one is a fixed forged coupler yoke, and the other one is a rotary forged coupler yoke. The fixed coupler draft gear draft gear adopts the fixed coupler yoke, as shown in FIG. 1, the coupler 11 is connected with a draft gear 15 in the fixed coupler yoke 14 by a follower 13, a coupler yoke pin 12 is penetrated between the coupler 11 and the fixed coupler yoke 14 to connect the coupler 11 and the fixed coupler yoke 14, and an inner end surface of the fixed coupler yoke 14, which is in contact with a bottom surface of the buffer 15, is a bearing surface. The rotatable coupler draft gear draft gear adopts the rotatable coupler yoke, as shown in FIG. 2, the coupler 21 is connected with a buffer 25 in the rotary coupler yoke 24 by a follower 23, a coupler yoke shaft 22 is penetrated between the coupler 21 and the rotatable coupler yoke 24 to connect the coupler 21 and the rotatable coupler yoke 24, and an inner end surface of the rotatable coupler yoke 24, which is in contact with a bottom surface of the buffer 25, is a bearing surface. The coupler yokes mainly bear traction loads in use. Both the bearing surfaces 10 of the fixed coupler yoke 14 and the rotatable coupler yoke 24 are the flat surfaces, as shown in FIG. 3 and FIG. 4, the structure is weak in local strength, therefore, the crack and the fracture on the coupler yokes used for the railway wagons are increased obviously along with the acceleration of the running speed and the traction tonnage of the railway carriages, thereby affecting the transportation efficiency and the travelling safety seriously.